Solar power is becoming increasingly popular as a source of renewable energy as advances in panel efficiency and manufacturing techniques have driven down the cost per kilowatt. This has led to double-digit annual growth in solar installs and projections of even greater growth in the future. Another factor driving growth has been the availability of solar leases, power purchase agreements, and other financial products that allow customers to have solar systems installed with little or no money down. Also, in jurisdictions that allow net metering, excess power is sold back to the utility by reverse flow through the homeowner's power meter, further increasing the value proposition of solar.
Solar installation companies normally attempt to maximize the energy generating capacity of the array on the sun-facing portion of the roof up to the homeowner or business owner's level of electricity consumption. One problem, however, that often arises with rooftop installations is that roofs may contain one or more sewer gas exhaust pipes, also called drain waste vent pipes or drain waste vents. In some cases these pipes may protrude from the portion of the roof surface best suited for the solar array in an area that would otherwise be desirable to place a solar panel. To deal with this issue, project planners and installers often are forced to design and install the PV array to bypass these obstructions leaving a gap in the array and potentially limiting the number of panels that could otherwise be installed.
FIG. 1 illustrates this problem. FIG. 1 shows a portion of a residential roof 100 with installed solar array 200, which includes 23 individual solar panels 200. As used herein, the terms “module” and “panel” will be used interchangeably to refer to a solar or photovoltaic panel, which can include a string of solar cells encased in a frame or other protective structure that converts impinging photons into electrical current. As shown in array 200 of FIG. 1, there is no panel at spot 205 due to the presence of sewer gas exhaust vent 300. Although in FIG. 1 vent 300 is shown near the middle of the top row of solar panels, it should be appreciated that in practical application, vent 300 may exist nearly anywhere in roof 100 and displace a panel in array 200 leaving a hole somewhere in the middle or a gap along either side. Moreover, even though only one vent 300 is shown in FIG. 1, it is not uncommon to have two or more vents clustered in a single roof above the positions of the waste water lines, particularly in larger homes.
Solar panel array 200 is shown in FIG. 1 in a portrait or “North-South” orientation. In practice, arrays may be installed using an East-West or landscape orientation, or even at some angle in between portrait and landscape.
In addition to detracting from the aesthetics of the install, each gap in the PV array that could have otherwise supported a solar panel represents less revenue for the array owner—whether it's the homeowner or a panel installer/leaser—in an amount equivalent to multiple times the cost of the installed panel. If the average install is about five kilowatts and each panel is capable of generating 250 Watts, as much as five percent of the solar potential could be lost on an install with only one missing panel. If the array is an area that receives on average 5 hours of sunlight per day over the course of a year, this amounts to a loss of nearly 7,000 kilowatt hours in 20 years (assuming 75% efficiency).
Unfortunately, drain waste vent pipes cannot be removed because they serve an important function. They equalize atmospheric pressure to the sewer stack so that shower, tub, sink and toilet drains will all drain properly. They also allow flammable and potentially harmful sewer gases to vent above the building so that they do not accumulate within any living space inside the building. Although there are alternatives to roof venting, such as air admittance valves (AAVs), so-called Durgo valves or Studor vents, they are not in widespread use. These are one-way mechanical vents that eliminate the need for conventional roof venting. A discharge of wastewater, such as from a toilet flush causes the AAV to open, releasing the vacuum and allowing air to enter the plumbing system for proper drainage to occur. Such valves are more commonly used in Europe and are even prohibited by code in some jurisdictions, which may explain why roof vents are essentially ubiquitous in the United States. Also, replacing existing sewer gas venting with AAVs within the house is not a viable solution because it would significantly increase the time and cost of a PV system install.
FIG. 2 shows a close-up perspective view of sewer gas roof vent 300 depicted in FIG. 1. Vent 300 includes a protruding metal or PVC vent pipe 301 with pipe opening 302. Although not shown in the Figure, pipe 301 typically runs down to either the sewer stack within the residence or into one of the wastewater drainage pipes that feeds into the stack somewhere before it reaches the stack. In order to prevent water leakage, flashing plate 310 is usually slid down over pipe 301 from the open end through an opening in rubber collar 312. Flashing plate 310 may also have raised portion 311 to compensate for the pitch of the roof (i.e., the pipe does not penetrate flashing plate 310 normal to its surface, but rather at an angle off of normal specified by 90 degrees minus the pitch of the roof). In some cases raised portion 311 may be eliminated and rubber collar 312 will instead be shaped to compensate for roof pitch. In a shingled roof, such as that depicted in FIG. 2, the top and optionally the side portions of flashing plate 310 may be tucked underneath the surrounding roof shingles so that water running down the roof will run over the flashing plate without leaking through the roof.
It is possible on certain homes that no flashing plate is present. This could be due, for example, to the addition of a new roof, poor original construction, or non-standard repairs. In such cases, a large bead of caulk, tar, or other sealant may be placed around the opening in the roof where vent pipe 301 penetrates the roof to prevent water from leaking through the roof.
FIG. 3 shows an isolation perspective view of a flashing plate such as that shown in FIGS. 1 and 2; FIG. 4 is a side view of the exhaust pipe and flashing plate on a roof with an existing solar panel array. Flashing plate 310 is typically constructed from sheet metal such as aluminum, steel, or other suitable durable material. As discussed above, plate 310 may have raised portion 311 that creates a horizontal or substantially horizontal pedestal for attaching rubber collar 312. Collar 312 has opening 313 sized such that it creates a waterproof friction fit with pipe 301 when slid over pipe 301, thereby preventing the ingress of water.
FIG. 4 shows flashing plate 310 on roof 100 with solar panel array 200. Solar panel array 200 stops down-roof from plate 310 and pipe 301 because pipe 301 extends higher than the array. In FIG. 4, array 200 is installed on roof 100 in a strutless configuration using a height-adjustable mounting assembly comprising mounting puck 211, adjustable leveling screw 212, and male groove connector 212 that clips into grove 251 formed in panel frame 250. As can be seen in FIG. 4, the presence of exhaust pipe 301 prevents placement of a solar panel over the roof in the area where vent 300 is located. Therefore, it would be desirable to provide roof venting in a manner that allows placement of solar panels over areas being used for exhaust venting without substantially impeding exhausting venting and with minimal complication and expense.